Back supports including pliant members adapted to be positioned across the front of a back member of an automobile seat to support the dorso-lumbar curve of the spine of a motorist are priorly known, for example, from U.S. Pat. No. 2,831,533, issued Apr. 22, 1958. Such back supports are generally directed toward adding rigidity to the spine by the application of a convex support surface thereto. In the employment of such prior art back supports, the fulcrum about which the upper legs turn, as the automobile bounces up and down, is in the area of the dorso lumbar curve. A forceful straightening of the dorso-lumbar curve, as viewed by some medical authorities, often percipitates pain in the lower back and legs. In accordance with these authorities, the proper forward curve of the spine, or lumbar lordosis, lessens the intradical pressure, i.e. the tendency for a disc of the spinal column to bulge and press against a nerve.
The prior art back supports are designed to relieve discomfort associated with bone and disc structures of the motorist's spinal column, while the present invention is based upon the view that driving discomfort is largely a problem associated with soft tissues (muscles and ligaments of the lower back). More particularly, that the motorist's discomfort is caused by the compressive and distractive forces applied to such soft tissues when an automobile bounces up and down during an extended driving period. To minimize such forces, the present invention includes a back support carriage freely movable in a generally vertical direction so as to maintain continuous, large area contact with the motorist's back, even when the automobile is bouncing up and down. As a result of such continuous, large area contact, the back of the motorist moves as a supported, substantially rigid unit; the fulcrum about which the upper legs turn as the automobile bounces up and down is in the area of the posterior; and a major portion of the compressive and distractive forces resulting from the automobile bouncing up and down, are absorbed by muscles and ligaments of the motorist's buttocks and legs.